Double layer of insulation - vapor barrier

[tadowler]

I am converting my attic into storage space and in the next few years hope to convert it to a living space.

I have 2x8 floor joists and replaced the loose fill fiberglass insulation with 2 layers of Comfort Therm batt insulation.

On the bottom layer I placed the vapor barrier next to the drywall (from the ceiling below).

On the top layer I faced the vapor barrier up and they laid plywood on top of it.

I now think I should have used an unfaced batt for my second layer. I can take the plywood up (I used screws) to put it down.

Here are my questions:

1) Should I put unfaced batts down as my second layer or can I just slice/puncture the vapor barrier with a utility knife?

2) Do you think this really is a problem if I leave it "as is"?

Thanks for the help!

[suemarkp]

A similar thing was done in my house. The people insulated the attic area for some reason, but left all the attic venting open. No point insulating when you've got a bunch of vents letting in cold air.

I think they used the vapor barrier as an easy way to mount insulation -- they didn't know what it was for. So I had walls and floors with vapor barriers on both sides of the insulation. I've cut most of the vapor barriers with a big X slash on each peice. I think it would be better to totally remove one of the two barriers, but then my insulation would have fallen down in the walls. I pulled the vapor barrier off the pieces on the top of the floor. It does pull off rather easily.

Every thing I've read says double vapor barriers are bad, but I saw no evidence of mold, dampness, or anything else between these vapor barriers. One answer could be the effectiveness of the barrier. Building felt and the tarpaper like kraft paper vapor barriers on insulation aren't a 100% barrier. They do breath somewhat. Plastic on the other hand is much more of a barrier. So if you have a plastic vapor barrier on either side of your insulation, I'd definitely remove one of them. Kraft paper types may be OK with both, but I'd at least cut one of them and remove one if possible.

[homebild]

Attic ventings are supposed to stay open at all times even when the floor is insulated.

The attic is supposed to stay as cold as the air outside the structure especially in cold climates otherwise you can create ice dams on the roof.

And as long as the attic is vented absolutely no vapor barrier is required on the attic insulation or in the ceiling at all.

A vapor diffusion retarder is only required when the walls or ceilings do not open to ventilated locations and in many cases the paint alone on the ciling below is all the vapor retarder one needs.

You need to remove the vapor barrier from the top layer of insulation.

The vapor barrier between the ceiling drywall and joists can stay but is uneccessary if the attic is ventilated.